Recently, in order to improve the warm-up characteristics of an internal combustion engine, a water pump is controlled to temporarily stop coolant circulation while the water-cooled internal combustion engine is being warmed up. For example, there is proposed a technology of intermittently flowing a coolant in coolant channels within the internal combustion engine by intermittently driving an electric pump force-feeding the coolant in the time the internal combustion engine is cold. This technology can reduce the heat release of the internal combustion engine while suppressing the increase in temperature in the periphery of the cylinder. Therefore, the warm-up of the internal combustion engine can be promoted (see Patent Document 1).
Also, conventionally, there is broadly known a control for switching between high or low of the lubricant pressure that is pressure fed by a lubricant pump driven in response to the temperature or the driving state of the internal combustion engine. For example, there is proposed a technology which controls the lubricant pressure to low when the internal combustion engine might not overheat in a low load and low speed region. Also, this technology finely estimates the overheat of the internal combustion engine and controls the lubricant pressure to the normal pressure, when the internal combustion engine is in a high load and high speed region. In this technology, while the load of the lubricant pump is reduced by the low lubricant pressure control, the increasing rate of the coolant temperature is reduced by changing the oil pressure to the normal oil pressure when the driving of a cooling fun is expected. Therefore, the operation period of the cooling fun can be reduced to the minimum. Since the load of the internal combustion engine is reduced, high mileage improvement effect can be ensured (see Patent Document 2). In the internal combustion engine performing such a control, the oil pressure within the lubricant path is controlled by closing or opening an electromagnetic valve. Such a system is referred to as two-stage hydraulic system. The two-stage hydraulic system can reduce the load of the lubricating oil pump when the viscosity of the lubricant is high by relieving lubricant in a low oil pressure state, and can stop ejecting the lubricant from a piston oil jet in the cold engine state. This allows reducing the load of the internal combustion engine and the mileage improvement by the improvement of the warm-up characteristics.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2006-214280    Patent Document 2: Japanese Unexamined Patent Application Publication No. 06-221127